Which of the following statements is the first step in the synthesis and secretion of T3 and T4?
Synthesis of thyroglobulin by the follicular cells
Oxidation of iodide by the follicular cells
Coupling of T1 and T2
lodide trapping by the follicular cells
The Correct Answer is D
a) Synthesis of thyroglobulin by the follicular cells: This occurs after iodide has been trapped and transported into the follicular lumen.
b) Oxidation of iodide by the follicular cells: This is a later step; iodide must first be trapped before it can be oxidized into iodine.
c) Coupling of T1 and T2: This is one of the final steps in T₃/T₄ synthesis where iodinated tyrosines are joined.
d) lodide trapping by the follicular cells
Iodide trapping is the first step, where follicular cells actively transport iodide from the bloodstream into the thyroid follicle using sodium-iodide symporters.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
a) The anterior pituitary produces testosterone from cholesterol and releases it when releasing hormones arrive from the hypothalamus.
Testosterone is produced in the testes, not the anterior pituitary.
b) The hypothalamus produces ADH and oxytocin which are stored in the posterior pituitary.
ADH and oxytocin are synthesized in the hypothalamus and then transported to and stored in the posterior pituitary until needed.
c) The posterior pituitary contains autonomic centers that exert neural control over the adrenal glands.
The hypothalamus, not the posterior pituitary, regulates the adrenal medulla via neural signals.
d) The thalamus produces ADH and oxytocin which are stored in the anterior pituitary.
The thalamus is a relay station for sensory signals, not a hormone-producing structure.
Correct Answer is A
Explanation
a) Hypothalamus: Oxytocin is synthesized by neurosecretory cells in the hypothalamus, specifically in the paraventricular and supraoptic nuclei. After production, it is transported down the axons of these neurons to the posterior pituitary gland, where it is stored and released into the bloodstream.
b) Somatic Nervous System: The somatic nervous system is part of the peripheral nervous system and controls voluntary skeletal muscle movements. It does not produce hormones and has no role in endocrine secretion.
c) Anterior Pituitary Gland: The anterior pituitary produces several hormones (like ACTH, GH, PRL, TSH, LH, and FSH), but oxytocin is not one of them. It is not produced by the anterior pituitary; instead, oxytocin is made in the hypothalamus and released from the posterior pituitary.
d) Posterior Pituitary Gland: While the posterior pituitary stores and releases oxytocin, it does not produce it. The production occurs in the hypothalamus, and the posterior pituitary acts as a storage and release site.
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